In disc drives, servo information is encoded on a disc during manufacture. During disc drive operation, the servo information is used to accurately position a read/write head on a particular data track that is to be read or written. The servo information is written or encoded onto the disc with a manufacturing machine called a servo track writer (STW) or multi-disc writer (MDW).
Unformatted discs are assembled with a central hub to form a disc-hub assembly. The central hub includes a bearing and a motor rotor. The disc-hub assembly is positioned in a MDW with the central hub adjacent a motor stator in the MDW and the bearing engaging a central spindle in the MDW. Once the disc-hub assembly is positioned on the rotor, the disc-hub assembly is spun while a write head in the MDW formats the discs with servo information. After formatting is complete, the formatted disc-hub assembly is removed from the MDW and can be assembled into a disc drive.
The fit between surfaces of the bearing and the spindle is extremely close. The bearing must be precisely aligned with the spindle when the bearing is slid into the spindle. The force used to advance the bearing toward the spindle is delicate and must be carefully limited to avoid damage when there is misalignment. The end of the bearing and/or the end of the spindle can be tapered or rounded to provide tactile feedback on alignment to a technician who is manually sliding the bearing onto the spindle.
As attempts are made to automate installation of the disc-hub assembly into the spindle by a robot, problems are encountered. Some existing robot end effector mechanisms have excessively high length and mass, resulting in excessive force when the bearing jams during installation. Some existing robot end effector mechanisms also have flexible connections to power sources such as air lines, hydraulic lines and electrical cables that exert forces on the end effector mechanism that exceed the delicate force required for installation or that adversely change alignment. When air lines are used, the air lines can introduce contaminated air into the clean room environment of the MDW. Existing end effector mechanisms lack a required delicate compliance and precise alignment at an interface with the forces fed back to the end effector mechanism by contacts between the bearing and the spindle.
A method and interface mechanism are needed to provide for robotic installation of disc-hub assemblies on spindles that provides both precise alignment and delicate force compliance. Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.